Polycone™ scanning system with multiple beams

Abstract

This invention relates to a pyramid polygon scanner wherein the differential scan length between multiple beams can be eliminated by tilting the beams with respect to the photoreceptor surface. Then the beam with the shorter scan lengths when the beams are normal to the photoreceptor, travel a greater distance before they impinge on the photoreceptor. At the start or end of scan the scan angle is not zero, so the scan lengths for the beams with the larger travel distances are increased by the extra distance multiplied by the tangent of the scan angle. At the proper tilt angle, all scan lengths at the photoreceptor are the same. Since the angular scan rate of all the beams are always the same, over the entire scan, the scan lengths of the individual beams will always be the same, at any fraction of the total scan. Thus the information written onto the photoreceptor by the multiple beams will be in alignment for all simultaneous beams.

What is claimed is: 
     
       1. In a rotating mirror scanning system including a multi-surface mirror assembly having plurality of surfaces and an axis of rotation, first and second light sources for introducing first and second sources of light beams toward said multi-surface mirror, said light beams being reflected in turn by each of said surfaces of said mirror, a first mirror placed in the path of said light beams reflected from said multi-surface mirrors, a second mirror placed in the path of said light beams reflected from said first mirror, said second mirror reflecting said light beams back to the same surface of said multi-surface mirror, the last reflection forming first and second scanning light beams of predetermined ranges of arc of one rotation of said multi-surface mirror, said multi-surface mirror assembly comprising a polygonal array of mirror facets, said mirror facets having a predetermined draft angle with respect to the axis of rotation of said multi-surface mirror assembly, and a photo-sensitive surface upon which said scanning light beams are to be raster drawn, said photo-sensitive surface being tilted with respect to said light beams to eliminate the differential scan length between said scanning light beams, wherein the scanning light beam with the shorter scan length, when the scanning light beams, are normal to said photosensitive surface, travels a greater distance before impinging on said photo-sensitive surface. 
     
     
       2. The mirror scanning system as set forth in claim 1 wherein said first and second light sources are tilted at a predetermined angle to one another. 
     
     
       3. The mirror scanning system as set forth in claim 1 wherein said first and second light sources are tilted at a predetermined angle α to one another, and wherein said photosensitive surface and said light beams are tilted at a predetermined angle β from one another such that two parallel, offset scan lines of equal scan length are generated at said photosensitive surface. 
     
     
       4. The mirror scanning system as set forth in claim 4 wherein the values of α and β have a predetermined relationship to one another for optimal generation of said parallel, offset scan lines of equal scan length.